Lubricants are generally applied in many metalworking operations. Such operations include stamping, drawing, forming, rolling, bending, cutting, grinding, punching, spinning, extruding, coining, hobbing, swagging and the like. The present invention concerns solid film (dry film) lubricants for such type of metalworking operations, and in particular, such operations as employed in automotive and appliance applications. In the automotive and appliance fields, the term "stamping" is used as a broad term to cover all press working operations on sheet metal, which operations may be further categorized as drawing, cutting, or coining. Automotive and appliance stamped parts may be produced by one of a combination of these three fundamental fabrication operations.
Metalworking lubricants, especially solid film (dry film) prelubes, facilitate these operations generally be reducing friction between the metal being worked and the element (tooling) employed for that process, and thus reducing the power for a given operation, reducing the wear of the surfaces of the work elements (tooling) employed that perform the necessary operation on the metals, and preventing sticking (adhesion) between the metal being worked and the work elements (tooling) operating thereon or between metal pieces during storage, handling or operations.
In automotive and appliance applications, the prevention of sticking (adhesion) between metal pieces and between such pieces and the work elements is of extreme importance. In addition, the use of specific metalworking lubricants such as solid film (dry film) prelubes significantly reduce or eliminate the production of scrap parts which often result from the failure of some lubricants to perform the necessary functions described above. Metalworking lubricants, including solid film (dry film) prelubes, often provide corrosion protection to the metal being processed and protection to such metal during storage and transportation.
In many metalworking processes, including automotive and appliance applications, coils or rolls of steel, in particular cold roll or specific types of galvanized steel sheets including hot dip galvanized, galvaneal and electrogalvanized, are cut into pieces call blanks. Such blanks are stamped or drawn to produce the desired finished parts. Such automotive parts formed by stamping or drawing, as these terms are generally used, include hoods, floor pans, deck lids, fenders, quarter panels, oil pans, fuel tanks, inner and outer door panels, tops and the like. Appliance parts formed by stamping and drawing include, as these terms are generally used, including washer tops, dryer tops, washer fronts, dryer fronts, top and front lids, oven liners, oven tops and dryer tumblers (backs and fronts), and the like. Prior to the use of lubricants known as prelubes (oil-based or solid film) the normal procedure was to apply and oil at the steel mill to such coils or rolls as a rust preventative (mill or slushing oils) prior to shipping to a processing site, such as a stamping plant. Between the steps of cutting such coils or rolls of steel into pieces called blanks and the stamping or drawing operation, such rust preventative oil would be removed by a cleaning operation (blank wash oil or alkaline cleaner) and a drawing lubricant then applied to the metal and at such times the work element (tooling) immediately prior to stamping or drawing. Such drawing lubricant is used to reduce friction and facilitate the metalworking operation to produce the desired finished part.
In recent times, the use of separate rust preventative oils and drawing lubricants has been in many operations replaced by the use of a single composition known as a prelube. Prelubes, whether oil-based or solid film, are generally applied at the steel mill during either temper rolling or inspection, as would be a rust preventative oil, prior to shipping. Such compositions are thus not intentionally removed from the metal until after the blanks are out and the parts formed. Thus, the use of such prelubes eliminates the tedious process of applying and removing the combination of rust preventative oils and drawing lubricants before further working with one composition (whether oil-based or solid film).
Prelubes thus must function as both a rust preventative and forming lubricant. In many instances, and particularly for automotive and appliance applications, a prelube must be removable with aqueous alkaline cleaners, non-staining to the metal and compatible with all other chemical compositions utilized in the processing operations in producing the products in question.
To prevent interference with future processing operations after the desired part is formed, it is necessary for all traces of the prelube composition to be effectively removed from the metal surface of the formed part. The advantages and efficiencies offered by prelubes, especially solid film lubricants, would be partially diminished or nullified if unusual or drastic elements were necessary to remove the prelube film from the finished part. In both the automotive and appliance industries, aqueous alkaline cleaners are the normal chemical compositions used to remove all lubricant compositions from the surfaces of the finished part.
These cleaners are usually powdered in form and composed of various mixtures of inorganic alkalais and biodegradable surfactants and amines. Such compositions are water soluble at the recommended dilutions and are strongly alkaline in nature (pH of 10.0-12.0). These cleaners are heavy duty in nature and designed in concept to effectively remove all traces of processing lubricants and fluids from a wide variety of metallic surface including those composed of ferrous steel, zinc, zinc-aluminum, zinc-iron and aluminum alloys. Finished parts are cleaned in a variety of cleaning systems using spray, immersion and combinations of both types. Such cleaner compositions are applied to parts for varying time increments, often 30 seconds to three minutes for spray systems and 1.0 to 5.0 minutes for immersion systems. Such cleaner compositions effectively operate over a wide temperature application range. Finished appliance parts are cleaned at temperatures varying from 140.degree.-190.degree. F. Automotive parts have been traditionally cleaned over a temperature range of 120.degree. F. to 145.degree. F.
Newer chemical compositions are now being used on a variety of automotive finished parts at lower temperatures, varying from 105.degree. F. to 125.degree. F. Such alkaline cleaner compositions allow for better economics associated with lower operating costs, and furthermore, the lower temperatures offer benefits in being more compatible with the variety of galvanized steels used to produce finished parts and such temperatures also are more compatible with future processing operations beyond the cleaning system. Many prelube compositions may contain chemical constituents that cannot be easily removed with such alkaline cleaners, thereby creating serious detrimental effects on all future processing operations and effectively limiting their use.
One major purpose and advantage of the present invention is the improved cleanability and removability for a solid film (dry film) prelube in both automotive and appliance industries at the lower temperature ranges of 120.degree. to 140.degree. F. and yet the maintenance of all other desired performance properties associated with such invention on a wide variety of metal substrates including ferrous, zinc-coated and non-ferrous for automotive and appliance industries.
Concerning metal staining, steel coils or rolls coated with prelube compositions may be stored for long periods of time before their use as bases for finished parts. Many chemical constituents of such prelube compositions can oxidize to varying degrees during those storage periods, and the oxidation reaction by-products can adversely affect the metal surface. For instance, the oxidation of hydrocarbon oil components to fatty acid by-products can stain, discolor and damage some forms of prelube substrates. Appliance and automotive industries require prelube compositions that will protect metal substrates during these potential storage periods against such oxidation conditions and effectively be non-staining.
Concerning the compatibility with other processing chemical compositions, many parts formed in automotive and appliance industries often have severe bends formed during the metalworking operations. These severe bends may have exceedingly tight radii such as in hem flanges where traces of prelube compositions can become entrapped. Thus, although the prelube compositions may be effectively removed from all exposed part surfaces, the entrapped portions may remain and be volatilized and released by subsequent processing operations. This potential release of the prelube composition necessitates that such compositions be compatible with cathodic electrocoat paint primers and bonding body adhesives used in automotive industries and porcelain enamel operations in the appliance industries. Many automotive finished parts are now being attached together by the use of bonding adhesives where welding methods are no longer suitable or desirable.
Appliance parts are often coated with porcelain enamel coatings to improve quality and durability of such finished parts. Most appliance and automotive formed parts are coming into contact with processing chemical compositions after the metalworking operation, and thus the prelube compositions improve their overall utilization and efficiency by being compatible with such processing compositions.
The majority of prelubes used commercially in the automotive and appliance industries today are compositions composed of petroleum hydrocarbon oils and additives and such compositions are fluid at ambient temperatures. Because of their fluid nature, these hydrocarbon oil-base compositions can drain off metal surfaces (depending on substrate orientation), become unevenly distributed on metal substrate surfaces due to capillary action or tend to pool or collect in hem flange areas becoming heavily concentrated in such areas. All of these conditions can have a drastic effect on prelube performance as the uniformity of the film on the metal substrate is critical to corrosion protection and the necessary lubrication for successful forming. Thus, the automotive and appliance industries demand a prelube that provides the desirable film uniformity that will provide adequate corrosion protection during the long term conditions of storage and transit, and furthermore, provide the critical film strength and performance demanded for successful forming operations, especially those required for severe drawing operations.
Further, with these hydrocarbon oil-based prelube compositions, housekeeping and cleanliness are extremely hard to maintain, both at the steel manufacturers where the product is applied and at the forming plant where the composition is used. These compositions leak onto tooling surfaces, machine surfaces and onto the floor creating hazardous work environments for all employees involved. Such compositions often contaminate floor waste trenches and plant waste treatment stream. Often these prelube compositions can volatilize into the plant environment creating health hazards and safety concerns. These oil-based compositions can often create dermatitis among workers exposed to such compositions for varying periods of time. Thus, at least the automotive and appliance industries demand a prelube that reduces or eliminates these problems.
In addition, a prelube composition that can be used at reduced levels and still provide the necessary performance parameters of corrosion protection and forming lubrication would be highly desirable. In the automotive and appliance industries, such oil-based prelube automotive and appliance applied at coverage rates up to 1,000-2,000 mg/ft.sup.2. The automotive and appliance industries desire a prelube composition that offers all the necessary benefits but will offer such benefits at a lower coating weight (coverage rate), thus improving the overall cost efficiency of that forming operation.
In addition, a prelube composition must be compatible with the current waste treatment processes being used to treat waste lubricants. The automotive and appliance industries desire a prelube that will be compatible with the current treatment processes and furthermore, offer some advantages to those processes.
It is an object of the present invention to provide a metalworking lubricant, and more particularly a solid dry film prelube that provides all of the foregoing desirable characteristics, and advantages especially improved low temperature cleanability, for all metalworking applications but especially for the automotive and appliance industries. It is a further object of the present invention to provide a method of lubricating various types of metal substrates, particularly cold roll steel and a variety of galvanized substrates including hot dip galvanized, electrogalvanized, galvaneal and galvalume, for all stamping and drawing operations especially those of the automotive and appliance industries, that provides all of the foregoing desired advantages. These and other objects of the invention are described below.